ADC Noise / Jitter Problem STM32F4

epalaima · ‎2016-07-12

Posted on July 13, 2016 at 00:04

I am using ADC's on the STM32F4 discovery board to read control values for my program from potentiometers and I am having problems where these inputs are very noisy, and cause my control values to modulate quite noticeably.

I sending DC to the ADC from the middle leg of a pot, the other two legs being connected to the board's 3.3v out and to ground respectively. I also have added some capacitors from the middle leg to ground, which seemed to help a little bit, but not much. I am using an oscilloscope and it seems that the noise is being caused by the ADC itself, since whenever I disconnect the middle pin from the ADC the noise drops considerably.

Can anybody suggest a solution to this issue? I am trying to use the STM32F4 for audio purposes and the noise is considerably lowering the quality of the audio coming out.

#noise #solution #!stm32 #adc

AvaTar · ‎2016-07-12

Posted on July 13, 2016 at 08:02

Keep the wiring short, and make sure the resistor value matches the ADC input impedance. I've successfully used values between 2k and 10k.

The higher the impedance and the longer the wires, the more susceptible to EMI.

raptorhal2 · ‎2016-07-13

Posted on July 13, 2016 at 16:06

When the ADC samples the input voltage, a sample and hold capacitor is charged up. The signal current during this time can cause the observed ''noise'' when the signal source is not of low impedance. Try increasing the sampling cycles.

Cheers, Hal